Question

which is the end of our solar system

Answer 1

Beyond the fringes of the Kuiper belt is the Oort Cloud. Unlike the orbits of the planets and the Kuiper Belt, which arepretty flat like a disk, It's a giant spherical shell surrounding the sun, planets, and Kuiper Belt Objects. Like a big bubble with thick walls around our solar system.

Answer 2

To state the obvious, 'nature is natural'. So shouldn't we explain nature in a natural way? Aren't the best answers the ones that are naturally simple?
To define where our solar system's boundaries end, let's use nature's own principle of proportions - a comparative relationship between components of different sizes and/or amounts that are properly balanced and symmetrical. 
 
Our solar system is a set of moving components ( the orbits of planets, comets, asteroids etc.) that are spaced in a particular order. This order will result in a non-random organized system.
 
Every system has the central component; the primary component; and the extremities or boundaries. To express those components in human form, they are: the brain; the heart; and the hands and feet.
 
For our solar system, the components are: the sun; the earth; and the outermost planet (dwarf planet) - Pluto. But, the orbit of Pluto ( where the planetary disk ends) is not where the solar system's boundaries end, we must go out farther - much, much farther. So given: Pi = 3.14159 and A, B, C, D, E, F and G.
 
Where;
A) sun radius = 6.9645 x 10^8 m.
 
B) earth radius = 6.378 x 10^6 m.
 
C) earth Aphelion = 1.521 x 10^11 m.
 
D) distance to Pluto from sun's center = 6.0 x 10^12 m.
 
E) temperature at top of sun's photosphere = 4000K.
 
F) Cosmic Microwave Background Radiation (CMBR) = 2.725K .
 
G) distance to Kuiper Belt = 1.6608 x 10^13 m.
 
Then;
* 2 x (A)^2 / B = C 
 
* 4 x (pi)^2 x (C) = D
 
* (C)^2 / 2 (A) = G

* (A) x (E)^2 / (F)^2 = 1.5006 x 10^15 m  or  (1,000 AU) x (100,000 AU) square root = 10,000 AU - the perfect 'Mean of two Extreme' distances to the Oort cloud. It's also the distance at which the temperature at the sun's core (1.6 x 10^7 K) diminishes, and is in equilibrium with the CMBR temperature. Hence effectively, the end of the solar system.